A D.C. ambulance that shut down while rushing a gunshot victim to the hospital last month had a clogged fuel filter screen, a preliminary inquiry determined, and the fire department announced that it will remove the devices from more than a dozen emergency vehicles.

Fire officials initially blamed the failure on an exhaust filter required by the Environmental Protection Agency to ease hazardous emissions. Those devices, which when clogged can cause engines to shut down, have drawn complaints from fire departments around the country for breakdowns and cumbersome maintenance schedules.

Acting D.C. Fire Chief John Donnelly said the manufacturer, Illinois-based Navistar, has agreed to remove the screens for free. The fire department has 94 ambulances in its fleet, but only 12 to 15 International-brand ambulances are affected.

“I’m glad they got to the bottom of it,” said Edward Smith, the head of D.C. firefighters union Local 36. “If this fix is what’s needed to avoid a shutdown during a response, we welcome it with open arms.”

Questions arose May 29 when an ambulance stalled taking 34-year-old Nathaniel McRae from Southeast Washington to Howard University Hospital. McRae had been shot by D.C. police officers after a carjacking, and he had to be transferred to another ambulance after the breakdown. He died shortly after arriving at the hospital; officials said the seven-minute delay did not contribute to his death.

After D.C. fire officials blamed the EPA-mandated emissions system for the breakdown, the federal agency defended its program and said problems can be avoided with proper maintenance. The system is designed to turn off an engine if the exhaust filter becomes clogged, forcing the vehicle to stop and go through an automatic cleaning process called regeneration.

A series of warning lights are supposed to let drivers know that shutdown is near but allow for plenty of time to complete an emergency call. Donnelly said that the only lights that flashed on May­ 29 showed imminent, catastrophic engine failure.

City officials said computer software in the ambulance falsely read the filter failure as a regeneration issue and triggered the shutdown. Donnelly said that software is being reprogrammed.

An EPA spokeswoman, Alisha Johnson, said the filter system is not subject to federal emissions regulations and can safely be removed.

Navistar said in a statement that it concurs the problem was not related to the exhaust filter or regeneration. But company mechanics do not agree that the problem has been identified, according to the statement.

Types of first responders

“The specific cause remains undetermined as we continue to work with D.C. fire and our local dealer on the investigation,” the statement said.